This invention relates to heat transfer and more particularly to a heat sink hold-down with fan-module attach location.
A number of approaches to heat sink hold down design have been used traditionally, including the examples described below:
FIG. 1 is a cross-sectional view of a traditional glue-on heat sink 101 attached to processor chip 102 with adhesive 103, which also acts as a thermally conducting interface. Processor chip 102 is typically mounted to bolster plate 104, which provides rigid mechanical support. Glue-on heat sinks have limited ability to hold on to the chip during a shock load. Using adhesive for thermal conduction compromises heat transfer compared to compression type heat sink attachment.
FIG. 2A is a cross-sectional view of a traditional shoulder screw/spring heat sink held under compression to a processor chip. Springs 201 are captured between heat sink base 202 and screw heads 203. When screws 204 are attached to bolster plate 104, the spring compression between screw heads 203 and heat sink base 202 loads heat sink 202 onto processor chip 102. Shoulder screw/spring heat sinks require a large amount of heat sink base space for mounting hardware. During installation they can cause uneven loading on the chip. Additionally, the screw assemblies are intrusive to air flow paths.
FIG. 2B is a cross-sectional view of a traditional low-profile spring-attach heat sink hold-down. Spring 211, which is rigidly mounted to bolster plate 104 and presses on the base of heat sink 212 against processor chip 102, has clearance slots for each heat sink fin. Low-profile spring-attach heat sink hold-down hardware is unobtrusive, but allows no place for mounting a fan to the top of the heat sink. It is also difficult to remove if chip replacement is required. Additionally it blocks air flow over the heat sink base.
FIG. 2C is a cross-sectional view of a traditional high-profile spring-heat sink hold-down. Spring 221 is rigidly mounted to bolster plate 104 and presses on the tops of the fins of heat sink 222. Alternatively, this traditional approach uses a screw running between the fins to transfer the load from spring 221 directly onto the base of heat sink 222. High profile springs intrude on the ability to mount a cooling fan on top of the heat sink.
It would be desirable in the art to provide a heat sink hold down system and method that minimize intrusion into the heat sink base space and into cooling air flow, that advantageously provide a location for mounting an optional fan, that load the chip essentially uniformly, and that allow easy removal to access the chip if required.
In accordance with a first embodiment disclosed herein, a system for heat sink hold-down is provided. The system comprises a heat source; and a heat sink hold-down assembly. The heat sink hold-down assembly comprises a bolster plate operable to rigidly support the heat source and a heat sink. The heat sink comprises a heat sink base operable to press the heat source against the bolster plate and to transfer heat from the heat source, and a longitudinal post having a first end and a second end opposite from the first end, which is attached to the heat sink base substantially orthogonally near the center of said heat sink base. The post is operable to transfer a longitudinal compressive force substantially symmetrically to the heat sink base. The heat sink hold-down assembly further comprises a lever spring contacting near its midpoint the second end of the post. The lever spring is operable to apply a compressive force to the second end of the post in response to a bending moment. The heat sink hold-down assembly further comprises a cap rigidly coupled to the bolster plate and coupled to the lever spring near the two ends of the lever spring. The cap is operable to apply a bending moment to the lever spring.
In accordance with another embodiment disclosed herein, a method of heat transfer using a heat sink hold down assembly is provided. The method comprises attaching a first surface of a heat source onto a surface of a bolster plate and positioning a heat sink, such that a first surface of a heat sink base of the heat sink is in surface contact with a second surface opposite the first surface of the heat source. A longitudinal post having a first end and a second end opposite from the first end is attached at its first end substantially orthogonally to the second surface opposite the first surface of the heat sink base. The method further comprises applying longitudinal compressive force to the second end of the post in response to a bending moment of a lever spring in contact with the second end. The method further comprises transferring the longitudinal compressive force substantially symmetrically to the heat sink base, thereby holding the heat source rigidly under compression between the heat sink base and the bolster plate. The method further comprises transferring heat from the heat source through the heat sink into ambient air.
In accordance with another embodiment disclosed herein, a system for heat sink hold-down is provided. The system comprises means for attaching a first surface of a heat source onto a surface of a bolster plate, and means for positioning a heat sink, such that a first surface of a heat sink base of the heat sink is in surface contact with a second surface opposite said first surface of the heat source, and such that a longitudinal post having a first end and a second end opposite from the first end is attached at the first end substantially orthogonally to the second surface opposite the first surface of the heat sink base. The system further comprises means for applying longitudinal compressive force to the second end of the post in response to a bending moment of a lever spring in contact with the second end, and means for transferring the longitudinal compressive force substantially symmetrically to the heat sink base, thereby holding the heat source rigidly under compression between the heat sink base and the bolster plate. The system further comprises means for transferring heat from the heat source through the heat sink into ambient air.